Observation of unusual optical transitions in thin-film Cu(In,Ga)Se2 solar cells.

In this paper, we examine photoluminescence spectra of Cu(In,Ga)Se(2) (CIGS) via temperature-dependent and power-dependent photoluminescence (PL). Donor-acceptor pair (DAP) transition, near-band-edge transition were identified by their activation energies. S-shaped displacement of peak position was observed and was attributed to carrier confinement caused by potential fluctuation. This coincides well with the obtained activation energy at low temperature. We also present a model for transition from V(Se) to V(In) and to V(Cu) which illustrates competing mechanisms between DAPs recombinations.

Study of InN epitaxial films and nanorods grown on GaN template by RF-MOMBE.

This paper reports on high-quality InN materials prepared on a GaN template using radio-frequency metalorganic molecular beam epitaxy. We also discuss the structural and electro-optical properties of InN nanorods/films. The X-ray diffraction peaks of InN(0002) and InN(0004) were identified from their spectra, indicating that the (0001)-oriented hexagonal InN was epitaxially grown on the GaN template. Scanning electron microscopic images of the surface morphology revealed a two-dimensional growth at a rate of approximately 0.85 µm/h. Cross-sectional transmission electron microscopy images identified a sharp InN/GaN interface and a clear epitaxial orientation relationship of [0001]InN // [0001]GaN and ( 2¯110)InN // ( 2¯110)GaN. The optical properties of wurtzite InN nanorods were determined according to the photoluminescence, revealing a band gap of 0.77 eV.

Study of surface morphology control and investigation of hexagonal indium nitride nanorods grown on GaN/sapphire substrate.

Heteroepitaxial growth of metal-catalyst-free indium nitride (InN) nanorods on GaN/sapphire substrates by radio-frequency metal-organic molecular beam epitaxy (RF-MOMBE) system was investigated. We found that different N/In flow ratios together with the growth temperatures greatly influenced the surface morphology of InN nanorods and their structural properties. The InN nanorods have been characterized in detail using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). Optical property was evaluated by photoluminescence (PL) measurements. At lower growth temperatures, InN nanorods were successfully grown. A pronounced two-dimensional growth mode was observed at higher growth temperature of 500 degrees C, and these films showed preferred orientation along the c-axis. XRD patterns and SEM images reveal that InN nanorods has high quality wurtzite structure with FWHM approaching 900 arcsec, and they have uniform diameters of about 150 nm and length of about 800 nm. Meanwhile, no metallic droplet was observed at the end of the nanostructured InN, and this is strong evidence that the nanorods are grown via the self-catalyst process. The PL peak at 0.8 eV is attributed to the quantum confinement and Moss-Burstein effects. These observations provide some valuable insights into the physical-chemical process for manufacturing InN nanorods devices.

Observation of unusual optical transitions in thin-film Cu(In,Ga)Se2 solar cells.

In this paper, we examine photoluminescence spectra of Cu(In,Ga)Se(2) (CIGS) via temperature-dependent and power-dependent photoluminescence (PL). Donor-acceptor pair (DAP) transition, near-band-edge transition were identified by their activation energies. S-shaped displacement of peak position was observed and was attributed to carrier confinement caused by potential fluctuation. This coincides well with the obtained activation energy at low temperature. We also present a model for transition from V(Se) to V(In) and to V(Cu) which illustrates competing mechanisms between DAPs recombinations.